1. Field of the Invention
The present invention relates to a photosensitive material used to form a polymer image, and an image forming method that employs it. More particularly it is concerned with a photosensitive material having a photosensitive and heat-developable layer, and, in particular, a photosensitive material capable of forming a polymer image having a superior contrast, value and chroma, and an image forming method that employs it.
2. Related Background Art
Energies used to form or record an image include light, sound, electricity, magnetism, heat, radiations such as electron rays and X-rays, and chemical energy, among which, in particular, widely used are light, electricity, heat energy, or a combination of any of these.
For example, a image forming method that employs the combination of light energy with chemical energy includes a silver salt photographic process and a method in which a diazo copying paper is used. The method that employs the combination of light energy with electric energy includes an electrophotographic system. The method that utilizes heat energy includes a method in which a thermo-sensitive recording paper or transfer recording paper is used. On the other hand, known as the method that utilizes electric energy is a method in which an electrostatic recording paper, electrothermal recording paper, or electrosensitive recording paper is used.
Of the above image forming methods, a silver salt photographic process can obtain an image having a high resolution. The silver salt photographic process, however, requires developing and fixing treatments that use complicated liquid compositions, or a drying treatment of an image (or a print).
Now, development is energetically made on image forming methods that can form an image through a simple processing.
For example, U.S. Pat. No. 4,629,676 teaches a method in which a polymerization reaction under dry (thermal) conditions is caused by a photosensitive reaction of silver halide that acts as a trigger, to form an image comprising a polymer.
Japanese Unexamined Patent Publication No. 62-70836 also discloses a method which comprises forming a latent image comprising silver metal produced from silver halide by imagewise exposure, and converting, under heating, a reducing agent into an oxidized product having a polymerization inhibitory power different from that of said reducing agent by utilizing a catalytic action of the above silver metal, thereby producing a difference in the polymerization inhibitory power between the reducing agent and the resulting oxidized product and also causing a thermal polymerization reaction utilizing a thermopolymerization initiator, thus forming a polymer image according to the difference in the polymerization inhibitory power.
In these methods, however, black silver which is formed by the metallic silver sometimes remains in the polymer image formed, and in that occasion an attempt to obtain a color image other than a black image may cause the mixing of a black color of a silver image into a color image to produce a dark color, resulting in the color image unsatisfactory in value and chroma.
Even in the case when no black silver remains in the polymer image, the photosensitive silver halide remains in the polymer image, and hence the color image may result in a color image unsatisfactory in that its value and chroma are not stable with time.
U.S. Pat. No. 4,649,098 discloses a method in which a reducing agent having a polymerization inhibitory power, contained in a layer containing a photosensitive silver halide, is formed into an oxidized product by imagewise consumption of itself (at exposed areas) in the course of the developing of silver halide, and then, after the reducing agent has been diffused and transferred by heating to a photopolymerizable layer on which the above layer containing a photosensitive silver halide is laminated face-to-face, light energy is uniformly applied (whole areal exposure) from the outside to cause photopolymerization at the part of the photopolymerizable layer opposing to the part (imagewise exposed area) at which the reducing agent in the above layer containing a photosensitive silver halide has been consumed, thus forming a polymer image.
The above method has the advantage that neither the black silver formed by the metallic silver nor the photosensitive silver halide remains in the polymer image formed and therefore the color image having superiority in the value, chroma and stability with time can be obtained even in the color image. It, however, is difficult to obtain a polymer image having a sufficient contrast. More specifically, the reducing agent used in the above method is in itself a reducing agent that acts as a polymerization inhibitor and turns not to act as the polymerization inhibitor after reducing silver halide. Hence, when the reducing agent at the imagewise exposed area of the layer containing a photosensitive silver halide is not sufficiently converted into an oxidized product, any sufficient polymerization can not be achieved at the part of the photopolymerizable layer opposing to the above imagewise exposed area. However, an attempt to apply a sufficient amount of heat energy in carrying out development so that the reducing agent in the imagewise exposed area may be sufficiently converted into an oxidized product, causes and oxidationreduction reaction even in an imagewise unexposed area. On the other hand, an attempt to apply the heat energy in a reduced amount in carrying out development so that the oxidation-reduction reduction may not be caused at the imagewise exposed area, results in no sufficient conversion into the oxidized product at the imagewise exposed area. Since the part of the photopolymerizable layer opposing to the imagewise exposed area of the layer containing a photosensitive silver halide can be polymerized with difficulty, light energy must be applied in a large amount upon carrying out the whole areal exposure, so that, with increase in the amount of applying the light energy, unnecessary polymerization may also take place at the part of the photopolymerizable layer opposing to the imagewise unexposed area of the layer containing a photosensitive silver halide, finally obtaining no polymer image having a sufficient contrast.
In addition, Japanese Unexamined Patent Publication No. 55-50246 discloses a photosensitive material comprising a support and a photopolymerizable composition layer, a transparent intermediate layer and a heat-development photosensitive composition layer which are laminated on the support, and a method which comprises subjecting the heat-development photosensitive composition layer to heat development to form a black silver image, followed by whole areal exposure from the heat-development photosensitive composition layer side to form a polymer image in the photopolymerizable composition layer, according to a difference in the amount of the light having been transmitted through the heat-developable and photosensitive composition layer.
In the above method, a constitution is taken such that the heat-development photosensitive composition layer and photopolymerizable composition layer are separated via an intermediate film, so that neither the black silver formed by the metallic silver nor the photosensitive silver halide remains in the polymer image formed. Thus the method has the advantage that the color image to be obtained can be a color image having superiority in value, chroma and stability with time, but is still insufficient in obtaining a polymer image having a sufficient contrast.
To discuss more specifically, in the above method, the contrast of the polymer image depends only on the difference in the amount of the light that has been transmitted through the heat-development photosensitive composition layer, and the difference between the amount of the light transmitted through an imagewise exposed area and the amount of the light transmitted through an imagewise unexposed area. In order to make close to 0% the amount of the light transmitted through the imagewise exposed area, measures can be taken to increase the amounts of the silver halide and organic silver salt in the heat-development photosensitive composition layer or to make large the layer thickness. This, however, decreases also the amount of the light transmitted through the imagewise unexposed area, consequently making small also the difference between the amounts of the light transmitted through the imagewise exposed area and imagewise unexposed area, so that no polymer image having a sufficient contrast can be obtained.
Incidentally, in the image forming method of the present invention, a difference in polymerization inhibitory power between the reducing agent and oxidized product that have been transferred is further utilized in addition to the above-mentioned difference in the amounts of the light transmitted through the imagewise exposed area and imagewise unexposed area, so that a polymer image having a sufficient contrast can be obtained.
Aiming at making visible the polymer image obtained by the above methods and further forming it into a color image, for example, U.S. Pat. No. 4,649,098 further discloses various methods that utilize the difference in, for example, physical properties and between a polymerized area and an unpolymerized area. For example, disclosed are a method in which a treatment is made using a liquid that does not dissolve the polymerized area and dissolves the layer of the unpolymerized area, to dissolve out and remove the unpolymerized area (i.e., etching); a method in which, utilizing the difference in stickiness between the polymerized area and unpolymerized area, a sheet such as plastic film is adhered and thereafter peeled to separate the polymerized area from unpolymerized area under dry conditions (i.e., peeling-apart); in the case when a polymer image is formed into a color image, a method in which a photopolymerizable layer is previously colored with use of a pigment or dye, and then subjected to the above dissolving-out (i.e, the above etching) or peeling (i.e., the above peeling-apart) to form a color image, or a method in which, utilizing the stickiness at the unpolymerized area, a coloring powder is applied to make selective coloring (i.e., torning or inking), or, utilizing the difference in liquid-permeability between the polymerized area and unpolymerized area, the unpolymerized area is selectively dyed by treating it with a dye solution.
However, no polymer image having a sufficient contrast can be obtained in the conventional polymer image forming methods as discussed above, and hence, even with employment of any of the above methods for making the image visible or forming it into a color image, the visible image and color image which are obtained from such a polymer image can not have any sufficient contrast, and particularly it has been difficult to obtain highly detailed visible image and color image.